When counter-terrorism police raid homes and stop buses on busy motorways
three weeks before the opening ceremony people will inevitably ask if it has
anything to do with the Olympics.

Stopping a London-bound bus for four hours because someone has an electric cigarette is the kind of thing that probably could not happen at any other time.

But the police have been drumming the message into the public for some years now: “If you see or hear something that could be terrorist related, trust your instincts and call the confidential anti-terrorist hotline...your call could save lives.” The Americans put it somewhat more pithily: “If you see something, say something.”

In Britain they don’t specify what they mean any more but the kind of thing they have in mind is a neighbour moving large amounts of chemicals, someone swapping mobile sim cards and identities, young men meeting in a flat but not staying over night.

Young men in a dinghy close to the Olympic canoeing venue? Certainly. Smoke coming from a bag? It’s a judgment call but nebulisers are disconcerting to say the least. They are designed to look like smoke, that’s part of the trick.

Perhaps the reaction was over the top but “major incident protocols” have a momentum all of their own. Once someone high up has made such a designation, it’s difficult to stop everyone going through their paces even after it is clear that the incident is far from serious.

So what about the arrests in London? There is an admission from the security services that “everything is Olympics related” even when it isn’t.

The men arrested in Ealing and Stratford may not have been targeting the Olympics but the fact that the police had to move in is at least partly down the proximity of the games. No one wants to be diverting resources once they are under way.

That said, MI5 and Scotland Yard like to use the footballing analogy – “defending further up the pitch.”

Over the last couple of years police have begun to intervene at ever earlier stages of plotting, largely because they have better coverage of plotters but also because watching groups for long periods of time takes up resources that could be used elsewhere.

MI5, who do most of the watching and listening, have “executive liaison groups” or ELGs which have worked alongside the police since the 1990s to make joint decisions on how to balance public safety and intelligence gathering.

The longer an operation is allowed to run, the better the chances of gathering intelligence, but there comes a time when the watchers feel they are not going to gain anything new or the police fear that a bomb could go off.

Then they have to go through the doors. The extra element that has been added in recent years is the liaison between the police and the Crown Prosecution Service.

The listeners have a better idea of whether they can bring charges against the plotters based on what they have been discussing.

However, don’t expect to be told what it’s all about. The days when police officers talked openly to the press are now over.

Besides, the chances are the arrested individuals don’t know yet either. It takes several hours to process the individuals in the secure cells at Paddington Green in West London and conduct “safety interviews” – “is there anything we should know about that might harm someone?” – before they see their solicitors and the proper interviewing process gets underway.

Most of the men won’t answer a single question, on the advice of their solicitors, but the police will still go through a drawn-out “interview strategy” that involves putting information in front of them bit by bit over the course of several days.

Eventually they run out of time and have to charge or release. At that stage prosecution solicitors try to give an idea of what the case is about when they appear in magistrates’ court, for the benefit of the public, before the legal shutters come down again and the press can report nothing more until the case comes to trial.